Noncontact laser microsurgical apparatus

ABSTRACT

A noncontact laser microsurgical apparatus and method for marking a cornea of a patient&#39;s or donor&#39;s eye in transplanting surgery or keratoplasty, and in incising or excising the corneal tissue in keratotomy, and for tissue welding and for thermokeratoplasty. The noncontact laser microsurgical apparatus comprises a laser source and a projection optical system for converting laser beams emitted from the laser source into coaxially distributed beam spots on the cornea. The apparatus further includes a multiple-facet prismatic axicon lens system movably mounted for varying the distribution of the beam spots on the cornea. In a further embodiment of the method of the present invention, an adjustable mask pattern is inserted in the optical path of the laser source to selectively block certain portions of the laser beams to thereby impinge only selected areas of the cornea.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a microsurgical apparatus and, moreparticularly, a noncontact laser microsurgical apparatus adapted for usein cornea transplant surgery, keratoplasty, keratotomy, and othercorneal surgery techniques.

2. Description of the Related Art

Despite advances in corneal preservation and transplantation techniques,postoperative astigmatism remains the most important complicationlimiting visual acuity after a corneal transplantation.

In order to reduce such postoperative astigmatism, U.S. patentapplication Ser. No. 07/056,711 filed Jun. 2, 1987 entitled "A CorneaLaser-Cutting Apparatus", assigned to the same assignee as the presentapplication, discloses that trephination of either a donor cornea or arecipient cornea may be performed utilizing a laser cutting technique.

During penetrating keratoplasty, it is further necessary for a surgeonto align the circumferences of the donor corneal button and recipientcornea. To this end, there have been recently developed mechanicalmarking apparatuses such as those described in Pflugfelder et al. "ASuction Trephine Block for Marking Donor Corneal buttons," Arch.Ophthalmol., Vol. 106, Feb. 1988, and Gilbard et al. "A New Donor CorneaMarker and Punch for Penetrating Keratoplasty," Ophthalmic Surgery, Vol.18, No. 12, Dec. 1987.

However, such mechanical marking apparatuses directly contact anddistort the cornea such that the marking process is not always preciselyaccomplished and sometimes results in postkeratoplasty astigmatism.

In radial keratotomy, mechanical contact type surgical utensils as shownin U.S. Pat. No. 4,417,579 have been used to radially incise the corneaof a patient's eye. This surgical method is apt to cause strain and/ordeformation of the cornea, and also results in postoperativeastigmatism.

Noncontact microsurgery of the cornea would minimize distortion of thecornea tissue, as occurs in contact-type techniques, and would decreasethe likelihood of producing postoperative astigmatism. The use of lasersprovides the potential for such noncontact microsurgery.

Excimer lasers have been investigated in the past to produce linearcorneal incisions or excisions. The argon fluoride excimer laseremitting at 193 nm has been shown to produce sharp, smooth-walledcorneal cuts. More recently, the hydrogen fluoride, Q-switched Er:YAG,and Raman-shifted Nd:YAG lasers emitting at about 2.9 um (micro meters),which corresponds to the peak absorption wavelength of water, have beenexperimentally used to produce linear corneal incisions or excisions.

Industrial laser cutting by focusing the beam into a ring has beenproposed as a method for drilling large diameter holes. The axicon, adiverging prismatic lens, has been used for such industrial purposes. Anaxicon system has been used by Beckman & Associates to study cornealtrephination with a carbon dioxide laser. This experimentation isdescribed in an article entitled "Limbectomies, Keratectomies andKerastomies Performed With a Rapid-Pulsed Carbon Dioxide Laser,"American Journal of Ophthalmology, Vol. 71, No. 6, (June 1971). In thisarticle, Beckman et al. describe the use of an axicon lens incombination with a focusing lens to form an "optical trephine" andperform various corneal experiments with animal's. The diameter of thetrephine was governed by the focal length of the focusing lens in theseexperiments. Therefore, to vary the diameter of the annular beam it wasnecessary to change the focusing lens which acted to change the width ofthe annular ring and, thus, varied the amount of tissue incised orexcised by the laser. Moreover, changing the focusing lens requires atime consuming process for each patient or donor. In addition, theoptical system proposed in the Beckman et al. article requires the useof multiple focusing lenses of different focal length.

Accordingly, it is an object of the present invention to provide anoncontact laser microsurgical apparatus and method of using the samewhich substantially eliminates strain and/or deformation on a corneaduring and after trephination.

Yet another object of the present invention is to provide a noncontactlaser microsurgical apparatus and surgical method which is capable ofmarking a recipient cornea and a donor corneal button with a suturetrack during keratoplasty, and which incises or excises selectedportions of a cornea radially and/or paraxially during keratotomy.

Still another object of the present invention is to provide a noncontactlaser microsurgical apparatus and surgical method which is capable ofperforming thermokeratoplasty for curing corneal refractive error and/orastigmatism of a patient's eye.

It is still another object of the present invention to provide anoncontact laser microsurgical apparatus and method capable ofsurgically "welding donor tissue or synthetic material and recipientcorneal tissue together thereby eliminating the necessity of suturingthe donor and recipient parts to one another in penetrating andepikeratoplasty procedures.

It is still a further object of the present invention to provide anoncontact laser microsurgical apparatus and method wherein selectedareas of the cornea may be caused to shrink so as to change thecurvature of the natural lens thereby curing or alleviating cornealrefractive error and/or asigmatism.

Additional objects and advantages of the invention will be set forth inthe description which follows, and in part will be obvious from thedescription, or may be learned by practice of the invention. The objectsand advantages of the invention may be realized and attained by means ofthe instrumentalities and combinations particularly pointed out in theappended claims.

SUMMARY OF THE INVENTION

To achieve the foregoing objects, and in accordance with the purposes ofthe invention as embodied and broadly described herein, the noncontactlaser microsurgical apparatus of the present invention comprises meansfor generating laser beams; and means for projecting the laser beamsonto a cornea. The projection means defines an optical axis and includesmeans for converging the laser beams. The projecting means furtherincludes axicon optical means for forming the projected beams into aplurality of paraxially distributed spots on the cornea, and means forvarying the radial position of the spots.

Preferably, the converging means includes a focusing lens and the axiconoptical means includes at least one multiple-facet prismatic ("MFP")axicon lens mounted for movement along the optical axis of theprojecting means.

The generating means may comprise an infrared pulse laser beam generatorwith a preferred wavelength of about 1.3-3.3 um. Also, an ultra-violetlaser source may be used such as an Argon fluoride laser emitting at 193nm.

The projecting means preferably includes beam expander means forenlarging the radius of the laser beam emerging from the generatingmeans.

The apparatus may also include aiming means for projecting visible laserbeams onto the cornea substantially coincident with the positions atwhich the laser beams projected through the axicon means impinge thecornea. The optical axis of the aiming means preferably overlaps with atleast a portion of the optical axis of the projecting means. Preferably,the aiming means includes a visible laser beam source, and a mirrorobliquely interposed between the beam expander means and the convergingmeans for reflecting the visible laser beams and allowing the laserbeams from the generating means to pass therethrough.

The apparatus of the present invention may also include mask meansdisposed in the optical axis for selectively blocking portions of theprojected laser beams while transmitting the remaining portions of theprojected laser beams therethrough. In this manner incisions orexcisions in the corneal tissue may be made only in selected areas ofthe cornea corresponding to the transmitting portions of the mask means.

The present invention also provides a microsurgical method for ablatingthe cornea in selected areas by appropriate use of the disclosedapparatus. Moreover, by careful selection of the laser generating meansthe corneal tissue may be heated only sufficiently to cause shrinkage ofthe tissue in selected areas to alleviate astigmatism and/or cornealrefractive error. Furthermore, by appropriate control of the selectedlaser generating means donor and recipient corneal tissue may be heatedin abutting areas to cause the disparate tissue to adhere to one anotherin the manner of a surgical weld to thereby eliminate the need forsutures.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate presently preferred embodimentsand methods of the invention and, together with the general descriptiongiven above and the detailed description of the preferred embodimentsand method given below, serve to explain the principles of theinvention. In the drawings:

FIG. 1 illustrates an optical system arrangement of a non-contact lasermicrosurgical apparatus incorporating the teachings of the presentinvention;

FIG. 2A is a plan view of a concave MFP axicon lens;

FIG. 2B is a cross-sectional view of the MFP axicon lens shown in FIG.2A;

FIG. 3A is a plan view of a convex MFP axicon lens;

FIG. 3B is a side view of the MFP axicon lens shown in FIG. 3A;

FIG. 4 illustrates a donor cornea holding device which may be used withthe apparatus and method of the present invention;

FIG. 5 is a plan view of a donor cornea marked by the apparatus of thepresent invention with spots defining a suture track;

FIG. 6 is a plan view of an alignment of a donor corneal button with arecipient cornea with spot marks defining a suture track in each;

FIG. 7 is a cross-sectional view of the alignment shown in FIG. 6;

FIG. 8 is a cross-sectional view of a cornea of a patient's eye markedwith incisions formed during radial keratotomy;

FIG. 9 illustrates a plan view of the eye shown in FIG. 8;

FIG. 10 illustrates a plan view of a patient's eye which has beensubjected to curved keratotomy;

FIG. 11 illustrates one embodiment of a mask means which may be usedwith the present invention;

FIG. 12 illustrates the angular orientation of the apertures defined bythe masked means of FIG. 11;

FIG. 13 illustrates a cutaway side view of a portion of the corneawherein portions of the stroma of the cornea have been treated bythermokeratoplasty;

FIG. 14 illustrates a front view of an eye which has been treated inselected areas utilizing the method and apparatus of the presentinvention with mask means;

FIG. 15 illustrates another embodiment of the mask means of the presentinvention;

FIG. 16 illustrates still another embodiment of the mask means of thepresent invention;

FIG. 17 is a cutaway side view of a portion of a cornea ablated by usingthe method and apparatus of the present invention and which illustratesthe configuration of the cuts in the cornea which may be made utilizingthe mask means of FIGS. 15 and 16;

FIG. 18 illustrates still another embodiment of the mask means of thepresent invention;

FIG. 19 illustrates the fully open position of the mask means of FIG.18;

FIG. 20 illustrates the fully closed position of the mask means of FIG.18; and

FIG. 21 illustrates the relationship between the incised or exciseddepth of cuts made in the stroma and the circumferential position ofannularly shaped laser beams projected by the mask means of FIG. 18.

DESCRIPTION OF THE PREFERRED EMBODIMENTS AND METHOD

Reference will now be made in detail to the presently preferredembodiments and method of the invention as illustrated in theaccompanying drawings in which like reference characters designate likeor corresponding parts throughout the several drawings.

An optical delivery system of a noncontact laser microsurgical apparatusincorporating the teachings of the present invention includes means forgenerating laser beams.

As illustrated in FIG. 1 and embodied herein, the generating means ofapparatus 10 comprises a laser source 11 which generates pulsed laserbeams that are capable of ablating the tissue of a living organ, i.e., acornea. Lasers which meet the requirements described above may includeHF (Hydrogen Fluoride) lasers and Er-YAG (Erbium-Yttrium AluminumGarnet) lasers which emit infrared pulses having wavelengths of about2.0 to about 3.0 um, and preferably about 2.9 um, and which have a pulseduration of less than 200 ns and an energy flux of greater than about250 mj/cm². Also operable with the present invention are ArF (ArgonFluoride) lasers which produce an ultra-violet laser beam havingwavelengths of less than about 200 nm with a pulse duration of about10-23 ns and an energy flux of about 70 mj/cm². Laser source 11 isconnected to a radiation control switch 11a. When the control switch ismoved to the "on" position laser source 11 generates infrared pulsedbeams. Radiation control switch 11a is preferably capable of controllingthe energy of the pulse beams by insertion of a neutral density filter(not shown) in a transmitting path thereof.

In instances where it is desirable to heat the corneal tissue withoutcausing ablation, the laser source selected may be an C.W.HF, orHolmium, or Nd:YAG laser emitting at a wavelength of 1.3-3.3 um, a pulseduration of greater than 200 n sec, and an energy flux of about 250mJ/cm².

In accordance with the present invention, the apparatus includes meansfor projecting the laser beams along an optical axis onto the cornea. Asembodied herein, the projecting means includes a beam expander means,generally referred to as 13, for expanding the laser beam generated bylaser source 11. Beam expander means 13 includes a concave lens 14 and aconvex lens 15. Laser beams emerging from convex lens 15 are formed inparallel and are in turn projected along optical axis O₁. The beamexpander means may also comprise a variable diverging beam expandercomprised of a conventional zooming optical system or a pair of movableconvex-concave axicon lenses described in the above-mentioned U.S.patent application Ser. No. 056,711.

In accordance with the present invention, the apparatus includes meansfor converging the projected laser beams onto the cornea. As embodiedherein, the converging means includes a condensing and focusing lens 17which functions to condense and focus light passing therethrough onto afocal plane. The position of the focal plane is determined in accordancewith the geometry of the lens as will be well understood by thoseskilled in the art. Beam expander 13 also acts to increase the laserbeam diameter entering lens 17, thereby increasing the numericalaperture of the optical system. Consequently, the focal spot of the beamat the focal plane of lens 17 is reduced.

In accordance with a first embodiment of the present invention, theapparatus includes axicon optical means for forming the converged laserbeams into a plurality of paraxially distributed beam spots on thecornea. As embodied herein the axicon optical means may comprise amultiple-facet prismatic ("MFP") lens 18.

As shown in FIGS. 2A and 2B, axicon lens 18 may be configured withconcave multiple-facet prisms (eight-facet prisms, for example) whoseouter edges (prism bases) 100 are larger in width than the optical axisportion 102 thereof. Axicon lens 18 may also be configured with convexmultiple-facet prismatic lenses as shown in FIGS. 3A and 3B whose outeredges (prism bases) 100 are larger in width than optical axis portions102 thereof. With reference to FIG. 6, the multiple-facet prism functionof axicon lens 18 causes the converging laser beams emerging from lens18 to be formed into a plurality of paraxially distributed beam spots 61on cornea 31 of eye 30. The spots 61 are radially spaced from the apexof cornea 31 and from optical axis O₁. Preferably, the laser beams areconverged onto cornea 31 of eye 30 (a patient's eye or donor's eye ortissue held in the holding device shown in FIG. 4) after reflection by adichroic mirror 19 as shown in FIG. 1. As a result, cornea 31 is marked,excised, or incised by the laser beam energy at spots 61.

It is necessary to vary the cornea marking, excising, or incisingdiameters in keratoplasty and keratotomy. To this end, the presentinvention may include means for moving the axicon optical means alongthe optical axis O₁. Furthermore, in order to carry out curvedkeratotomy in accordance with the present invention, means may beprovided to rotate the axicon optical means about the optical axis.Furthermore, to perform radial keratotomy, means may be provided formoving the converging means along the optical axis.

As embodied herein, movement of the axicon optical means comprised ofMFP lens 18, and movement of the converging means comprised of focusinglens 17 along optical axis O₁, and rotation of MFP axicon lens 18 aboutoptical axis O₁, may be carried out by a known electro-mechanical device(not shown) which may comprise a combination of stepping motors, forexample, controlled by a microprocessor or minicomputer (not shown). Byway of example and not limitation, model no. SPH-35AB-006 steppingmotors manufactured by Tokyo Electronic Co., Ltd. may be used to moveMFP lens 18 and focusing lens 17.

In accordance with the present invention, the microsurgical apparatusincorporating the teachings of the present invention may include aimingmeans for projecting visible light beams onto the cornea substantiallycoincident with the positions at which the laser beams are to impingethe cornea. As embodied herein, the aiming means comprises an aimingsystem 20 which includes a He-Ne laser source 21 for generating visiblelight beams, beam expander means 22, and dichrotic beam combiner 16.Beam expander means 22 may comprise a concave lens 23 and a convex lens24. Dichrotic beam combiner 16 is positioned in optical axis O₁ and isselected such that it functions to reflect incident He-Ne laser beams,while laser beams from source 11 pass therethrough.

He-Ne laser beams from laser source 21 are enlarged in diameter byexpander means 22, whose output laser beams, in turn, are projected ontocondensing and focusing lens 17 after reflection by cold mirror 16.Thus, laser beams from source 21, which are reflected by mirror 16, arecoincident with a portion of optical axis O₁.

For observing the cornea and the He-Ne laser beams projected thereon,the noncontact laser microsurgical apparatus may also include viewingmeans comprised of an operation microscope 2, indicated by phantom linesin FIG. 1. The configuration and function of operation microscopes iswell known in the ophthalmology field, therefore, its detaileddescription is omitted. By way of example and not limitation, a modelno. OMS-600 microscope manufactured by TOPCON CORPORATION may be used.

An optical axis O₂ of operation microscope 2 is disposed to becoincident with a portion of optical axis O₁ of the noncontact lasermicrosurgical apparatus 10. In this configuration, mirror 19 functionsas a half mirror for the laser beams from source 21, but as a completemirror for the laser beams from source 11. An operator can determine anoptimum diameter size of the laser beams projected onto the cornea byobserving the laser beams from source 21 through operation microscope 2.

For marking a donor corneal button, the noncontact laser microsurgicalapparatus may be coupled to a donor cornea holding device 40 as shown inFIG. 4. Donor cornea holding device 40 is provided with a housing cover41 and a receiving pedestal 42. Housing cover 41 includes an "O"-ring 43disposed on an inner wall 44, and an annular magnet member 45. Receivingpedestal 42 includes a convex portion 46, a gas tube 47 extending fromthe center of the convex portion 46 to a pressure pump 49, a pressuregauge 48, and a magnet member 50 which is disposed opposite to andattracts the magnet member 45 of housing 41. In operation, a donorcornea or corneascleral tissue 51 is mounted on the receiving pedastal42 and the housing cover 41 is placed over button 51. Due to attractiveforces between magnet members 45 and 50, "O"-ring 43 presses the cornealbutton tightly to the housing pedestal 42. Pressurized gas or fluid issupplied to the underside of the corneal tissue 51 through the tube 47so that the donor tissue is maintained with a constant undersidepressure which may be controlled to correspond to the intraocularpressure of the live eye, about 15 mmHg-20 mmHg, by monitoring pressuregauge 48.

The steps of the method of the present invention for marking a cornea intransplanting surgery or keratoplasty can be carried out by using thenoncontact laser microsurgical apparatus as hereinbelow described.

(1) A donor cornea or corneascleral tissue 51 cut out from a donor eyeis mounted on the cornea holding device 40. The donor cornea ispressurized at normal intraocular pressure (15-20 mmHg) on the undersidethereof by the fluid supplied from pump 49 through tube 47.

(2) The cornea holding device 40 is coupled to the laser microsurgicalapparatus shown in FIG. 1 by appropriate mechanical means (not shown).

(3) Visible aiming laser light beams from source 21 are projected ontothe cornea of a patient or onto a donor cornea through beam expandermeans 22, cold mirror 16, condensing lens 17, MFP axicon lens 18, anddichroic mirror 19.

(4) The visible aiming laser beams projected onto the cornea areobserved through operation microscope 2. The diameter and position ofthe projected aiming laser beams are adjusted by moving the noncontactlaser microsurgical apparatus and the operation microscope in tandemalong optical axis O₂.

(5) Next, axicon lens 18 is moved along optical axis O₁ so that thediameter or radial positions of paraxially distributed aiming laser beamspots from source 21 is adjusted to the desired size.

(6) After the diameter or radial positions of aiming laser beam spotshas been set at an optimum size or radial position, control switch 11ais turned on and laser source 11 generates the infrared or ultravioletpulsed laser beams.

(7) The pulsed laser beams are projected onto the cornea through thebeam expander 13, cold mirror 16, condensing lens 17, MFP axicon lens 18and the dichroic mirror 19, respectively, to mark the donor cornea orcorneascleral tissue with spots 61 as shown in FIGS. 5 and 6. Whenirradiating laser energy is properly controlled, light-point marking inaccordance with this particular embodiment of the method of the presentinvention can be carried out on the epithelium of the donor cornea 51.

(8) The donor cornea may then be trimmed or cut about its periphery soas to match the diameter of a recipient hole in the recipient cornea andis then preserved. A noncontact laser microsurgical cutting apparatus asdisclosed in U.S. patent application Ser. No. 056,711, commonly assignedwith this application and incorporated herein by reference, may be usedto cut a donor corneal button and a recipient cornea.

(9) After the cornea holding device 40 has been removed from thenoncontact laser microsurgical apparatus, a recipient eye is set up asshown in FIG. 1. The recipient cornea is also subject to marking andcutting as stated in the above steps (3)-(8), provided, however, thatthe diameter and radial positions of the paraxially distributed beamspots 61 on the recipient cornea is made slightly larger than thediameter and radial positions of the beam spots 61 on the donor cornealbutton.

(10) Next, the donor corneal button 51 is aligned with the recipientcornea 52 by matching the paraxially distributed spots 61 as shown inFIG. 6. The cornea has epithelium 71, stroma 72, and endothelium 73 asshown in FIG. 7. The paraxially distributed spots 61 on the donorcorneal button 51 and recipient cornea 31 may be marked only on theepithelium 71, or through the epithelium, the Bowman's layer and to apredetermined depth (for example 100 um) into the stroma, to createsuture tracks.

(11) Suturing is then carried out through the paraxially distributeddots as indicated by dotted line 74 in FIG. 7.

By carrying out the steps of the first embodiment of the method of thepresent invention as described above, eight dots are marked on each ofthe donor corneal button 51 and the recipient cornea 31 as shown in FIG.6.

When sixteen spots are required to be marked, after the first markingsteps are carried out as described above, axicon lens 18 may be rotatedby a predetermined angle about optical axis O₁, for example 22.5°, tomark an additional 8 spots. Similarly, an additional eight suture tracksare marked on the recipient cornea 31 so that sixteen symmetrical spotsare marked on both the donor corneal button and the recipient cornea.

The noncontact laser microsurgical apparatus of the present inventionmay also be utilized in keratotomy, as will be described hereinbelow.

The diameter or radial positions of the distributed beam spots can beadjusted by moving MFP axicon lens 18 along optical axis O₁ as alreadyexplained hereinabove in connection with keratoplasty. Moreover, inradial keratotomy where the radial incisions or excisions made in thecornea extend outwardly from the apex of the cornea, the focal plane ofthe laser beams must be varied since the curvature of the cornea causesthe radial incision or excisions in the cornea to be formed at varyingdistances from the laser source as the incision or excision movesprogressively outward from the apex of the eye. Thus, to insure that thelaser beams are brought to focus in the correct focal planecorresponding to the varying depths or distances at different radialpositions on the cornea, the focal plane of the apparatus of the presentinvention is adjusted by moving condensing lens 17 along optical axisO₁.

In radial keratotomy, wherein incisions or excisions are produced in thestroma and are oriented radially from the center of the cornea to theouter edge of the cornea, the curvature of a cornea is measured inadvance by a keratometer so as to predict the distance of the focalplane of the laser beams at all radial positions on the cornea. Withreference to FIG. 8, after the initial focal points "C" have been set inthe upper portion of stroma 72, MFP axicon lens 18 is moved axially andpreferably continuously within a predetermined range along optical axisO₁ so that radial incisions or excisions in stroma 72 may be made alongthe curvature of the cornea from points "C" toward points "D" as shownin FIGS. 8 and 9, FIG. 8 being a cutaway side view of FIG. 9 along lines8--8. Simultaneously, condensing lens 17 is moved axially and preferablycontinuously along optical axis O₁ to adjust the focal plane of thelaser beams to correspond to the radial position of the cornea at whichthe incision or excision is being made.

Laser energy from source 11 may be set to a sufficient energy to ablateand incise or excise the tissue of stroma 72 to a desired depth "Δ".

In curved keratotomy, wherein the excisions or incisions in stroma 72are oriented as curved portions, i.e., as circumferential arcs spaced apredetermined and substantially constant radial distance from the apexor center of the cornea, MFP axicon lens 18 may be comprised of at leastone two-facet prismatic lens. After focal points "C" have been set instroma 72, MFP axicon lens 18 is rotated about optical axis O₁ within apredetermined rotating angle while laser source 11 is emitting beams ofsufficient energy to ablate the stroma, thereby producing incisions orexcisions in the stroma as illustrated in FIG. 10.

In another embodiment of curved keratotomy utilizing the apparatus andmethod of the present invention, MFP axicon lens 18 may be composed ofat least one MFP lens having more than two facets, eight facets forexample, which is rotatable about the optical axis O₁. Furthermore,apparatus 10 may include mask means, disposed between focusing andcondensing lens 17 and cold mirror 16, for selectively defining at leastone open aperture in optical axis O₁. In the present preferredembodiment, the mask means includes mask 25 having three mask units 26,27, and 28 as shown in FIG. 11. Mask units 26 and 27 each include a pairof transparent portions 26a, 27a configured as 120° fan-shaped apertureangles 110 for transmitting laser beams emerging from cold mirror 16therethrough, and a pair of opaque portions 26b, 27b configured as 60°fan-shaped aperture angles 112 for blocking the laser beams emergingfrom cold mirror 16.

In accordance with the present invention, means may be provided forrotating mask units 26 and 27 in opposite directions, designated byarrows "a" and "b" in FIG. 11, relative one another about optical axisO₁ to change aperture angles 110a and 112a within a prescribed range,for example, between 60°-120° as illustrated in FIG. 12. As embodiedherein the rotating means may comprise a stepping motor (not shown)controlled by a microprocessor (not shown). One skilled in the art willreadily identify such motors and controllers, and, since theconfiguration of these motors and controllers do not themselvesconstitute any portion of the present invention, a detailed descriptionis omitted. However, by way of example, a model no. SPH-35AB-006 typemotor manufactured by Tokyo Electric Co., Ltd. may be used. Also, anysuitable controller such as an IBM PC/AT may be used to control themotor.

The mask means may also include a mask unit 28 having a pair ofsemicircular portions 28a, 28b. Semicircular portion 28a is transparentto transmit laser beams therethrough, and semicircular portion 28b isopaque to the laser beams. Means may be provided to insert and removemask unit 28 within optical axis O₁ to selectively block a portion ofthe laser beams from source 11, the blocked portion corresponding to theposition of opaque semi-circular portion 28b. The mask units 26, 27 and28 are constructed to be able to rotate in unison about optical axis O₁to selectively position the apertures defined by masks 25 and 26 inoptical axis O₁.

In this embodiment, after aperture angles 110a and 112a have beenselected by individual opposite rotation of masks 25 and 26, and afterthe inclination angle β illustrated in FIG. 12 has been selected bycommon rotation about axis O₁ of masks 25 and 26 as a unit, the MFPaxicon lens 18 rotates continuously in predetermined minute steps aboutoptical axis O₁ for incising or excising the cornea.

The noncontact laser microsurgical apparatus and method of the presentinvention has further applications to thermokeratoplasty as will bedescribed hereinbelow.

In thermokeratoplasty, for curing corneal refractive errors, e.g.,hyperopia, myopia and/or astigmatism, laser source 11 may comprise aninfra-red pulse type laser that emits a laser pulse having wavelengthsof about 1.3 um to about 3.3 um. Laser source 11, in this embodiment,may comprise a Ho (Holmium) laser, for example, emitting at a wavelengthof about 2.1 um.

With reference to FIG. 13, in thermokeratoplasty for curing hyperopia,for example, after the focal points "C" have been set at points "e" withan optimum diameter and an optimum depth "Δ" in the stroma 72 byindependently moving focusing and condensing lens 17 and MFP axicon lens18 along optical axis O₁ as has been described above, the Ho lasersource 11 generates and projects the pulse laser beams onto the points"e".

Eight burns are formed instantly and simultaneously at the points "e"and cause shrinkage of the tissue of the stroma in the vicinity "f"around the points "e." The thermal effect of the laser causing shrinkageof the tissue about points "e" leads to a change of the shape of thecornea to alleviate hyperopia.

With reference to FIG. 14, in thermokeratoplasty for alleviatingastigmatism, mask unit 25 may be used to selectively define the angularposition b and the angle a, and to set the number of spots 61 projectedonto the points "e". The thermal effect of the laser and the resultingshrinkage of tissue in vicinity "f" lead to a change of the shape of thecornea to alleviate the astigmatism.

In the embodiments of the method and apparatus of the present inventiondescribed above, the tissue of the cornea is impinged with laser beamsof sufficient energy and for a sufficiently long time that the cornea isablated by causing the fluids comprising the corneal tissue to go fromsolid or liquid phases to a gaseous phase. Such ablation is termedphotovaporization when carried out using a hydrogen-fluoride shortpulsed, and photodecomposition when carried out using an argonfluorideexcimer laser.

In other embodiments of the surgical method of the present invention, itis desirable not to vaporize or decompose the corneal tissue. Since thecorneal tissue is comprised almost entirely of water, this means thatunder atmospheric pressure the temperature to which the corneal tissueis raised must be less than 100° C. This is best carried out with lasershaving longer pulse durations, such as a long-pulsed C.W.HF laser,Nd:YAG laser, or a Holmium laser each having pulse durations greaterthan 200 ns and an energy flux of about 250 mJ/cm².

The inventors herein have discovered that above 60° C., the cornealtissue becomes adhesive and will begin to shrink. Thus, in oneembodiment of the method of the present invention, selected areas of thecornea are impinged with laser beams having sufficient energy and for asufficient time to heat the corneal tissue to less than about 100° C. tothereby cause shrinkage of the corneal tissue in those selected areas.In this manner the shape of the cornea and the curvature of thecrystalline lens of the eye can be modified to alleviate astigmatismand/or corneal refractive error. Moreover, any of the embodiments of theapparatus of the present invention may be used in the practice of thismethod for shrinking corneal tissue to thereby control and define theselected areas of the cornea in which shrinkage is desirable.

In a further embodiment of the method of the present invention, where,during corneal transplant surgery, the donor cornea button has beenplaced in the recipient cornea, the abutting edges of the donor buttonand recipient cornea may be impinged with laser beams of sufficientenergy and duration to heat the abutting edges to between about 60°C.-85° C. For this embodiment it is desirable to use a laser sourcehaving a pulse duration of greater than about 200 ns, a frequency ofabout 2.0-3.0 um, and an energy flux less than about 250 mJ/cm². In thismanner, the tissue at the edges of the button and recipient hole becomeadhesive and attach to one another in a type of surgical weld therebyeliminating the need for sutures. This welding method may also beemployed in epi-keratoplasty to attach a piece of cornea-like tissueover a whole recipient cornea to act in the manner of a contact lens.This cornea-like tissue may be human, animal or synthetic.

In a second embodiment of the present invention, a conical axicon lens18' illustrated with the dot-dash line in FIG. 1 may used in place ofMFP axicon lens 18. In such an embodiment the conical axicon lens neednot be rotated about optical axis O₁ to perform curved keratotomybecause the conical axicon lens converts the laser beams exiting fromcondensing and focusing lens 17 into annular beams and projects themtoward the patient's cornea.

Each of FIGS. 15 and 16 illustrate alternative embodiments of the maskmeans. In both alternative embodiments of the mask means, two masks arespaced from one another on optical axis O₁. Each mask is identical inconfiguration. Therefore, only one of the masks, mask 130, isillustrated in FIGS. 15 and 16.

By way of example and not limitation, mask 130 may comprise a metalplate having two fan-shaped opaque portions 132 and 134, and side edges136 and 138 which are formed in a concave arc as shown in FIG. 15, or ina convex arc as shown in FIG. 16. Since the energy density of arc laserbeams emerging through the aperture defined by side edges 136 and 138decreases gradually along the radial direction of the arcs defined bythe side edges 136 and 138, the depth of the incised or excised cut onthe patient's cornea is shallowed gradually and smoothly at both endportions as shown in FIG. 17 such that delicate or subtle curvedkeratotomy may be carried out utilizing the method and apparatus of thepresent invention.

FIG. 18 illustrates a still further embodiment of the mask means.Therein, masks 150 and 152 having wedge shaped portions 154 and 156,respectively, may be moved simultaneously or individually in oppositedirections relative one another along arrows 158 and 160, respectively.In this manner, the aperture angle a defined by the edges of the wedgeportions 154 and 156 may be selected in a predetermined manner.Furthermore, masks 150 and 152 may be rotated individually or in unisonby any suitable motor or manual means about optical axis O₁ toselectively define the position angle b of the incised or excised cutson the cornea of the eye.

Utilizing the mask means illustrated in FIG. 18, masks 150 and 152 maybe moved towards each other along directions 158 and 160, respectively,during impingement of the cornea with laser beams. In FIG. 19, masks 150and 152 are in the fully open state such that no portion of the corneais blocked by wedge portions 154 and 156. As masks 150 and 152 are movedcloser together as illustrated in FIG. 18, wedge portions 154 and 156selectively block larger portions of the cornea from the laser beamsemitted by source 11. In FIG. 20, wedge portions 154 and 156 overlapeach other to fully block the cornea from any laser beams emitted bysource 11.

Utilizing the mask means illustrated in FIG. 18 in combination with aconical axicon lens, the annular laser beams P projected onto the corneaare changed in total emitted energy in accordance with thecircumferential position d as illustrated in FIG. 19. Therefore, theincised or excised depth D of the cuts made in the stroma are graduallychanged in depth to resemble a sine curve as illustrated in FIG. 21. Inthis manner, alleviation of corneal astigmatism may be carried out moredelicately and subtly utilizing the teachings of the present inventionto cure not only corneal astigmatism, but also corneal spherical powererror.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details, representative devices, andillustrative examples shown and described. Accordingly, departures maybe made from such details without departing from the spirit or scope ofthe general inventive concept as defined by the appended claims andtheir equivalents.

What is claimed is:
 1. A noncontact laser microsurgical apparatus,comprising:means for generating laser beams; means for projecting saidlaser beams toward a cornea, said projecting means defining an opticalaxis, and including:means for converging the laser beams onto thecornea; means including an axicon optical element for forming theconverged laser beams into a plurality of paraxially distributed beamspots on the cornea; and mask means having at least one mask forselectively defining at least one light transmissive aperture and atleast one opaque aperture along said optical axis of said projectingmeans.
 2. A noncontact laser microsurgical apparatus as in claim 1,wherein said mask means includes first and second masks spaced from oneanother and aligned on said optical axis, each said mask including atleast two fan-shaped light transmissive portions which define selectedopen angles therebetween when viewed along said optical axis, and meansfor rotating said first and second masks in opposite directions relativeone another to selectively adjust said selected open angles formedbetween said transparent portions of said masks.
 3. A contact lasermicrosurgical apparatus as in claim 1, wherein said axicon opticalelement includes an axicon lens having multiple prismatic facets.
 4. Anoncontact laser microsurgical apparatus as in claim 1, wherein saidprojecting means includes beam expander means for enlarging a radius ofsaid laser beams, and said converging means including a condensing lensfor focusing said laser beams on the cornea.
 5. A contact lasermicrosurgical apparatus as in claim 1, wherein said generating meansincludes an infrared laser beam generator.
 6. A noncontact lasermicrosurgical apparatus as in claim 1, wherein said generating meansincludes an ultraviolet laser beam generator.
 7. A noncontact lasermicrosurgical apparatus as in claim 1, further including aiming meansfor projecting visible light beams onto the cornea at positionssubstantially coincident with positions to be impinged by said laserbeams, and an optical axis of said aiming means overlapping with aportion of said optical axis of said projecting means.
 8. A noncontactlaser microsurgical apparatus as in claim 1, further including means foradjusting a radial position of said beam spots relative to an apex ofthe cornea.
 9. A noncontact laser microsurgical apparatus as in claim 1,further including means for moving said converging means along saidoptical axis of said projecting means.
 10. A noncontact lasermicrosurgical apparatus, comprising:means for generating laser beams;means for projecting said laser beams toward a cornea, said projectingmeans defining an optical axis, and including:means for converging thelaser beams onto the cornea; means including a conical axicon opticalelement for forming the converged laser beams into annularly shapedbeams; and mask means including at least one mask for selectivelyblocking at least one first arc-shaped portion of said annular-shapedlaser beams and for transmitting at least one second arc-shaped portionof said annularly-shaped laser beams to thereby impinge the cornea withsaid transmitted laser beams at selected positions corresponding to saidportion of said mask means through which said laser beams aretransmitted along said optical axis.
 11. A noncontact lasermicrosurgical apparatus as in claim 10, wherein said mask means forms atleast one aperture having a predetermined area for passing the laserbeams therethrough, and includes means for changing said area of saidaperture.
 12. A noncontact laser microsurgical apparatus,comprising:means for generating laser beams; means for projecting saidlaser beams toward a cornea, said projecting means defining an opticalaxis, and including:means for converging the laser beams onto thecornea; means including an axicon optical element for forming theconverged laser beams into annularly shaped beams; mask means includingfirst and second masks disposed along said optical axis; said first andsecond masks each having two fan-shaped opaque portions for selectivelyblocking two arc-shaped portions of said annularly-shaped laser beams,and two fan-shaped transparent portions for transmitting two arc-shapedportions of said annularly-shaped laser beams; and means for mountingsaid mask means relative to said optical axis such that said first andsecond masks may be rotated independently of one another to vary thesize of said arc-shaped portions of said laser beam passing through saidtransparent portions of said first and second masks.
 13. A noncontactlaser microsurgical apparatus as in claim 12, further including meansfor moving said converging means along said optical axis of saidprojecting means.
 14. A noncontact laser microsurgical apparatus as inclaim 12, including means for rotating said masks in unison toselectively adjust an angular position of said apertures about saidoptical axis.
 15. A noncontact laser microsurgical apparatus as in claim12, wherein said mask means further includes a third mask havingsemicircularly-shaped transparent and opaque portions for definingadditional patterns of said mask means.
 16. A noncontact lasermicrosurgical apparatus as in claim 15, including means for rotatablymounting said third mask along said optical axis.
 17. A noncontact lasermicrosurgical apparatus as in claim 12, wherein said axicon opticalelement includes a conical axicon lens having at least one conicalrefractive surface.
 18. A noncontact laser microsurgical apparatus as inclaim 12, wherein said projecting means includes beam expander means forenlarging a radius of said laser beams, and said converging meansincluding a condensing lens for focusing said laser beams on the cornea.19. A noncontact laser microsurgical apparatus as in claim 12, whereinsaid generating means includes an infrared laser beam generator.
 20. Anoncontact laser microsurgical apparatus as in claim 12, wherein saidgenerating means includes an ultraviolet laser beam generator.
 21. Anoncontact laser microsurgical apparatus as in claim 12, furtherincluding aiming means for projecting visible light beams onto thecornea at positions substantially coincident with positions to beimpinged by said laser beams, and an optical axis of said aiming meansoverlapping with a portion of said optical axis of said projectingmeans.
 22. A noncontact laser microsurgical apparatus as in claim 12,further including means for adjusting a radial position of said beamspots relative to an apex of the cornea.